Friction material



M y 195I H. w; SCHULTZ 2,553,215

FRICTION MATERIAL Filed Nov. 25, 1946 INVENTOR. HAROLD M 6/7 04 7'2 ATTOBA/EYS TEN OFFICE UNITED STATES FRICTION MATERIAL Harold W. Schultz, DaytonQOhio, assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application November 25, 1946, Serial No. 712,101

do; not arise with, normally dry clutches. may be explained by the fact that when a wet 2 Claims. (01. 26017.2) l 2 This inventionrelates to friction material and porosity which permits metering of a fluid thereisparticularly concerned with friction facings for through.

useiin-wet. clutches.

Wet clutches, that is, clutches running in oil orother fluids, present peculiar problems which This clutchbegins to engage, the fluid acts as a cushion between the clutch plates. This fluid must be accurate machining heretofore found necessary. It is therefore the primary object of this invention to provide a facing material for use in a wet clutch, or the like, which has the desired frictional characteristics together with a controlled A further object of the invention is to provide a method for forming said friction material wherein the porosity or metering action is assured through the precoating of the porous material used in the friction material with a predetermined quantity of binder prior to its incorporation with the remainder of the ingredients used properly disposed of or a slippage occurs which 1.0 in the complete mixture. persists over an appreciable period of time. When Another object of the invention is to provide a ducts; are provided in the. facings for leading the clutch facing material which may be molded and fluid. away. from the facing during engagement which includes cotton fiber or flock, round cork, thereof, the cost of the clutch is increased and in a binder having thermosetting propertiesand a .many cases, the control of theremoval of fluid is friction fortifyingagent.

not sufficiently accurate to permit smooth en- In carrying out the above object, it is a further gagementof the clutch members. object in some cases to use asbestos fiber and/or Wet clutches have definite advantages in that leather fiber as a substitute for the cotton flock .the operation thereof is generally smoother than or in some casesv in combination therewith.

withadry clutch sincethe fluid provides a cush- Further objects and adva s f the present ioning effect. Further the presence of fluid maininvention will be apparent from the following detains the clutch plates relatively cooler and inscription, reference being had to the accompanycreases the life thereof. For these reasons, a wet in drawing wherein preferred embodiments of clutch has advantages which far outweigh its, di'sthe present invention are clearly shown. advantages, which primarily are directed to the In the drawing: cost. The drawing shows a characteristic torque- I have formulated a material for use in a frictime curve for the preferred friction facing comtion facing used in connection with a wet clutch position. which has all of the desired frictional character- In the formation of friction material under the istics and which also acts as a metering means teachings of this disclosure, I pro-mix a binder per se for permitting controlled flow of the fluid with the other ingredients in separate batches from between the clutch plates during engagee by a predetermined q tity of binder mament thereof. This is accomplished through the terial is presentv adjace t the S ve a in redie ts use of a porous material in the facing per se Which which assures the proper distribution thereof in porous at rim eta d th flow of fluid t the. final article. In the preferred embodiment of through due to its peculiar nature but simultane- 35119 invention, cotton flock fiber is used as the ously permits a controlled flow that provides for porous element of the facing- This Cotton fl a cushioned, engagement of the plates, that is very is fi With a binder having thermosettmg smooth in operation and which permits. full enpropertles f m a fluid t whereby each fi .gagement within a relatively short period of time 40 of the 9 1S Coated n 1S und to the crossingwhereupon substantially-e41;ofithefiuld is:removed Over portlons of afiJacentfibersj In i f from between thejplatea ner a. porousv matnx is formed Wlnch will permit The facing is a formulation-of, the variousma- 252211 gg fiff iff fluld i g y fi' terials to. be describedin detail hereinafter which 2 e p 1a is mcorpom e m 18 to a metal backing acmg' may be molded and The other maJor lngredient of the facing is member for Strength and ngldlty a granulated or ground cork which is likewise prea relatively smooth surface at the frict on facing mixed with the binder in Somewhat different e free q O11 g f mdenieiloaelthel quantities after which the cork and the cotton helical or rad1al, which eliminates considerable are mixed When dry to form a homogeneous mass to which may be added a friction-fortifying material. This mixture is then molded and heated to a temperature sufiicient to cause partial polymerization thereof; that is to say, sufficient polymerization to hold the molded article together.

niarketed by the Irvington Varnish Company.

The next step is to place the molded facing on a cement coated steel disc or backing plate and heat under pressure to a temperature sufiicient to bond the facing to the plate and simultaneously to complete the polymerization of the binder used in the facing material.

More specifically, one form of the invention may be prepared as follows:

100 parts cotton flock is mixed thoroughly with 90 parts of a 20% (solids) solution of a phenol formaldehyde resin, and allowed to air dry for about one hour after which it is dried at 200 F. for 30 minutes. I

100 parts of granulated cork is thoroughly mixed with 50 parts of 20% (solids) solution of phenol-formaldehyde resin and is allowed to air dry for one hour after which it is dried at 200 F. for 30 minutes.

(All proportions expressed as parts by weight.)

These two compounds form the basis of the friction material and in the final compounding the proportions are 20 parts of prepared flock to 10 parts of prepared cork together with about three parts of a friction-fortifying material, preferably Cardolite dust (cashew nut resin). Cardolite is a trade name of a product made and It is essentially a dust made from polymerized cashew nut shell liquid (anacardic acid) and is available on the market in various grades of hardness, ranging from a rubbery consistency to a hard particle. All grades are suitable for friction fortification, according to the specific requirements of the application. This mixture is molded and cured for thirty minutes at 225 F. to form a facing which may then he placed on a metal backing that has preferably previously been given a coat of conventional cement whereupon the assembly is heated under pressure for 45 minutes at from BOO-315 F. to effect the final cure and bond.

The above formula is the preferred form of the V invention. It should be understood that the prepared mixture of cork and cotton flock may vary from 10 to 50 parts of cork to from 90 to 50 parts -of flock. Likewise the friction-fortifying material may vary from to 20 parts. In the matter of the binder, this'may vary from between 15 to 20 parts of resin which is preferably made up Y into a 20% (solids) solution for use with the flock. In the preparation of the cork, the resin may vary from 5-15 parts made up as a 20% (solids) solution. The total resin content obtained by adding the'resin used in the cork and fiock formulations yields a range of total resin of from 20 to 35 parts by weight (solids).

In place of Cardolite dust, other friction-fortifying or friction stabilizing agents, as they are termed, such as lead sulphide, carbon, metal powder, various salts or mixture thereof, etc., may be used in order to control the frictional characteristics of the finished product. In place of cotton fiber, I have found that asbestos fiber or leather fiber may be used either in part or in whole as is desired, which ingredients arepreheated with the resin solution in the manner already explained in connection with the cotton fiber.

The temperature control in the various drying and curing steps may also vary through wide ranges. For example, in the preparation step of .both the flock and the cork, air drying may be used entirely, dependent on time. Obviously, the

since no appreciable polymerization is necessary or desired the temperature of this step must be kept relatively low. In the second step, that is, the moldingof the facing material, the temperature should be held to between 200-225 F. This step is more critical since toohigha temperature will cause the binder to pass through a critical stage of polymerization and in this particular step only partial polymerization is desired. The final curing step, which is accomplished simultaneously with the bonding of the facing on the backing plate, may be performed at temperatures of 285-325" F., which are conventional temperatures for complete polymerization for phenol formaldehyde type resins.

In this connection, in place of phenol formaldehyde resin, cresol formaldehyde, or urea formaldehyde types of resin may be used. Likewise other resins, either thermosetting or thermoplastic, may be used if they will withstand the temperature of operation and will, upon final curing, have thermosetting properties either through polymerization or through mechanical vulcanization. The temperature of the plate during service is probably in the neighborhood of 350 F. at the surface since the oil in which the clutch runs is normally maintained at a temperature of 250 F. Thus any binder utilized must not soften at the temperature of operation and this is about the only limitation with respect to the binder.

In the material described herein, the cotton fibers act as the metering means to bleed off oil normally present at the engaging surfaces wherer by a cushioned engagement of the plates is obtained. It is apparent that considerable porosity must remain in the fiber portion of the facing to accomplish the end desired and it is for this reason that the preparation step of the fiber is important and should be accomplished separately from the preparation step of the cork. In other words, the separate mixing of the binder in predetermined quantities with the cork and with the fiber before the final mass is mixed is highly desirable since the control thus obtained permits the correct porosity in the final plate after fabrication of the facing. 7'

The accompanying curve shows torque plotted against time. The area under the curve is the total work expended upon initial engagement of clutch plates until the two plates are rotating without slip and at the same speed. The curve shows a low and constant torque buildup through this period which is desirable over erratic and fast buildups since operation is smooth and free from grabbing.

While the embodiments of the present invention as herein disclosed, constitute preferred forms, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows:

1. A molded composition of matter foruse as a wet clutch facing material comprising fiber, taken from the class consisting of cotton flock, leather fiber and asbestos fiber, to 50 parts,

ground cork 10 to 50 parts, a friction-fortifying material up to 20 parts consisting of dust made HAROLD W. SCHULTZ.

6 REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Fisher Nov. 21, 1922 Bastian Oct. 30, 1923 Harvey July 4, 1939 Denman Jan. 2, 1940- Kuzmick Sept. 23, 1941 Harvey Aug. 24, 1943 Batchelor Aug. 27, 1946 

1. A MOLDED COMPOSITION OF MATTERFOR USE AS A WET CLUTCH FACING MATERIAL COMPRISING FIBER, TAKEN FROM THE CLASS CONSISTING OF COTTON FLOCK, LEATHER FIBER AND ASBESTOS FIBER, 90 TO 50 PARTS, GROUND CORK 10 TO 50 PARTS, A FRICTION-FORTIFYING MATERIAL UP TO 20 PARTS CONSISTING OF DUST MADE FROM POLYMERIZED CASHEW NUT SHELL OIL, AND A BINDER FOR THE WHOLE IN QUANTITIES OF FROM 20 TO 35 PARTS (SOLIDS), SAID RESIN BEING TAKEN FROM THE CLASS CONSISTING OF PHENOL FORMALDEHYDE RESIN, CRESOL FORMALDEHYDE RESIN AND UREA FORMALDEHYDE 